The polyamides industry uses a whole range of monomers consisting of long-chain ω-amino acids, normally known as Nylon, characterized by the length of methylene chain (—CH2—)n separating two amide functional groups —CO—NH—. Thus it is that Nylon 6, Nylon 6,6, Nylon 6,10, Nylon 7, Nylon 8, Nylon 9, Nylon 11, Nylon 13, and the like, are known.
These monomers are, for example, manufactured by a chemical synthesis route using in particular, as starting material, C2 to C4 olefins, cycloalkanes or benzene but also castor oil (Nylon 11), erucic or lesquerolic oil (Nylon 13), and the like.
Current developments with regard to the environment are resulting in the use of natural starting materials originating from a renewal source being favored in the fields of energy and chemistry. This is the reason why some studies have been taken up to develop, industrially, processes using fatty acids/esters as starting material in the manufacture of these monomers.
This type of approach has only a few industrial examples. One of the rare examples of an industrial process using a fatty acid as starting material is that of the manufacture, from the ricinoleic acid extracted from castor oil, of 11-aminoundecanoic acid, which forms the basis of the synthesis of Rilsan 11®. This process is described in the work “Les Arocédés de Pétrochimie” [Petrochemical Processes] by A. Chauvel et al., which appeared in Editions Technip (1986). 11-Aminoundecanoic acid is obtained in several stages. The first consists of a methanolysis of castor oil in a basic medium, producing methyl ricinoleate, which is subsequently subjected to a pyrolysis in order to obtain, on the one hand, heptanaldehyde and, on the other hand, methyl undecylenate. The latter is converted to the acid form by hydrolysis. Subsequently, the acid formed is subjected to a hydrobromination to give the ω-brominated acid, which is converted by amination to 11-aminoundecanoic acid.
The process of the invention is targeted at the synthesis of 9-aminononanoic acid or 9-aminoazelaic acid corresponding to Nylon 9. As regards this specific monomer, mention may be made of the work “n-Nylons, Their Synthesis, Structure and Properties”, 1997, published by J. Wiley and Sons, chapter 2.9 (pages 381 to 389) of which is devoted to Nylon 9. This article summarizes the preparations and studies carried out with regard to the subject. Mention is made therein, on page 381, of the process developed by the former Soviet Union which has resulted in the commercialization of Pelargon®. Mention is also made therein, on page 384, of a process developed in Japan which uses oleic acid originating from soybean oil as starting material. The corresponding description makes reference to the work by A. Ravve “Organic Chemistry of Macromolecules” (1967) Marcel Dekker, Inc., part 15 of which is devoted to polyamides and which mentions, on page 279, the existence of such a process.
In order to be fully informed with regard to the state of the art on this subject, mention should be made of the numerous papers published by E. H. Pryde et al. between 1962 and 1975 in the Journal of the American Oil Chemists' Society—“Aldehydic Materials by the Ozonization of Vegetable Oils” Vol. 39, pages 496-500; “Pilot Run, Plant Design and Cost Analysis for Reductive Ozonolysis of Methyl Soyate” Vol. 49, pages 643-648 and R. B. Perkins et al. “Nylon-9 from Unsaturated Fatty Derivatives: Preparation and Characterization” JAOCS, Vol. 52, pages 473-477. It should be noted that the first of these papers also make reference, on page 498, to previous studies carried out by the Japanese authors H. Otsuki and H. Funahashi.
To summarize this state of the art targeted at the synthesis of “Nylon 9” from vegetable oils, a description may be given of the following simplified reaction mechanism applied to the oleic ester extracted from the oils by methanolysis:
Reductive OzonolysisH3C—(CH2)7—CH═CH—(CH2)7—COOCH3+(O3,H2)→HOC—(CH2)7—COOCH3+H3C—(CH2)7—COH
Reductive AminationHOC—(CH2)7—COOCH3+(NH3,H2)→H2N—(CH2)8—COOCH3+H2O
HydrolysisH2N—(CH2)8—COOCH3+H2O→H2N—(CH2)8—COOH+CH3OH.
However, this route, which is very attractive from the reaction viewpoint, exhibits a significant economic drawback consisting of the production, during the first stage, of a long-chain aldehyde (9 carbon atoms in total) which in practice cannot be recovered in value, in particular in the polymer industry relating to polyamides.